Work to be supported by this grant will continue to investigate the anatomy and physiology of the song control system of birds. Specific aims are to better understand, 1) the relation between production and perception of learned song; 2) brain asymmetries and sexual dimorphism that may occur in the perception of learned song; 3) the rules that govern the recognition of conspecific song and the preference that females show for the song of some individual birds; 4) the anatomical and physiological regulation of song learning; 5) the relation between pathways used for song learning and pathways governing other reproductive behaviors. Information on these matters should uncover interesting principles of brain function that can then be related to learning. The P.I. expects that these insights will be applicable to other systems, including vocal learning and brain function in humans. Information derived from these various related projects might also help understand how the newly discovered phenomenon of neuronal replacement in adult avian brain relates to how song learning circuits are organized. Health relatedness: The P.I. believes that the kinds of circuit plasticity that birds seem to use for learning -- neurite growth and retraction, formation and culling of synapses, neurogenesis - - will, once understood at the molecular level form the basis of inducible and controlled brain self-repair. In addition, a better understanding of the factors that restrict or encourage learning could be of great benefit to humans. The song learning system of birds is good material to study these matters.